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DISCUSSION OF STATE OF PREDICTIVE ART IN SUBSIDENCE ENGINEERING

THREE SEPARATE DISCUSSIONS ARE PRESENTED. (1) GRAY AND SALVER. EXPERIENCE ON THE MAGNITUDE OF SUBSIDENCE IN THE WESTERN PENNSYLVANIA BITUMINOUS COAL FIELDS, WHERE THE ROOM AND PILLAR SYSTEM OF MINING IS USED, IS COMPARED WITH THE AUTHORS' INFORMATION ON LONGWALL MINING IN EUROPE. DATA ARE PRESENTED TO CHALLENGE THE VIEW THAT ROOM AND PILLAR RETREAT MINING IS, IN EFFECT, A MODIFIED LONGWALL PANEL. IT IS ALSO SHOWN THAT OVER A 55-FT DEPTH A MINED SECTION WAS 4.5 FT SHALLOWER THAN AN ADJACENT UNMINED ONE, AS COMPARED WITH THE 6--7 FT THICKNESS OF THE EXTRACTED COAL. THIS DIFFERENCE, WHICH IS THE DIRECT RESULT OF SUBSIDENCE, INDICATES AN INCREASE IN VOLUME CAUSED BY FRACTURING AND REORIENTATION OF THE ROCK STRATA. (2) ALLEN. A METHOD REFERRED TO BY THE AUTHORS FOR PREDICTING MAXIMUM SUBSIDENCE BY RELATING IT TO THE SEAM THICKNESS AND PANEL WIDTH--DEPTH RATIO HAS RECENTLY BEEN SUPERCEDED BY ONE THAT TAKES WIDTH AND DEPTH INTO ACCOUNT SEPARATELY. (3) STOUT. HAVING JUST FINISHED A SECTION ON LEGAL ASPECTS OF SUBSIDENCE FOR THE NEW REVISION OF PEEL'S "MINING ENGINEERS HANDBOOK," THE WRITER REVIEWS EXISTING STATUTE LIABILITY IN THE LIGHT OF THE AUTHORS' FINDINGS.